Syn Breaking Change

[aurexav]

dtolnay/syn@957840e

https://github.com/paritytech/substrate/blob/master/frame/support/procedural/src/storage/parse.rs#L50

Which would cause

error[E0433]: failed to resolve: could not find `export` in `syn`
  --> /home/xavier/.cargo/git/checkouts/substrate-a7fa553ead635512/7314a78/frame/support/procedural/src/storage/parse.rs:50:37
   |
50 | impl<P: syn::export::ToTokens> syn::export::ToTokens for Opt<P> {
   |                                     ^^^^^^ could not find `export` in `syn`

error[E0433]: failed to resolve: could not find `export` in `syn`
  --> /home/xavier/.cargo/git/checkouts/substrate-a7fa553ead635512/7314a78/frame/support/procedural/src/storage/parse.rs:50:14
   |
50 | impl<P: syn::export::ToTokens> syn::export::ToTokens for Opt<P> {
   |              ^^^^^^ could not find `export` in `syn`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0433`.
error: could not compile `frame-support-procedural`

---

Workaround lock syn to 1.0.57

[VitalJeevanjot]

I have received this as well while following: https://substrate.dev/docs/en/tutorials/start-a-private-network/keygen